Chronic reductions in limb blood flow have important implications for both physical function and disease risk in humans. Presently, there is no information on the potential influence of regular exercise on basal limb blood flow in humans. Accordingly, the specific aims of the present proposal are to determine 1) whether the age-related reductions in basal whole-limb blood flow and vascular conductance observed in sedentary adults also occur in adults who perform regular aerobic exercise, 2) if regular resistance (strength) exercise is also associated with the attenuation of the age-related reductions in basal whole-limb blood flow and vascular conductance, and 3) if the postulated absence/attenuation of age-related decreases in limb blood flow in habitually-exercising adults are associated with maintenance of fat-free mass and/or metabolic rate with age. After extensive screening to establish eligibility, femoral blood flow (triplex ultrasound), arterial blood pressure, and femoral vascular conductance will be determined under supine resting conditions in groups of young, middle-aged, and older healthy men and women. Subjects will be sedentary, endurance-trained, or strength-trained. Muscle sympathetic nerve activity, cardiac output, leg oxygen consumption, plasma catecholamines, leg fat-free mass, and other measurements will also be obtained. The expected results will provide new and clinically important information concerning the role of habitual exercise on basal limb blood perfusion in adult humans and the underlying mechanisms. [unreadable] [unreadable]